Many people in the world live in countries where there is a severe shortage of hygienic potable water. People in these areas have to depend directly on ground water sources like wells, ponds and rivers. Often these water sources are contaminated by sewage, industrial effluents and agricultural byproducts. These areas are generally small villages that do not have municipal drinking water treatment plants. Hence these people have to treat the water themselves before consuming it. The water from these sources is often collected by the people in buckets or pots in small quantities like ten to twenty liters for potable consumption for a day's use. The most common method to produce clean water is boiling. However many people cannot afford to boil the water since it requires fuel like coal, or wood which are expensive and scarcely available.
These people often cannot depend on other methods of water purification like use of UV treatment devices or membrane filtration devices. This is because these devices require availability of electric power which is often not available on a continuous basis in these areas.
Some gravity fed water filters for domestic use have been described in the past. These purifiers use a suitable biocide to make the water microbiologically safe for drinking. The most commonly used biocides are halogen containing compounds. One group of commonly used halogen releasing compounds is trichloroisocyanuric acid (TCCA) and sodium dichloroisocyanurate (NaDCC). Another class of halogen releasing biocides are hydantoins and the most commonly used compound is 1-bromo-3-chloro-5,5-dimethyllhydantoin (BCDMH).
WO2006/006155 (Bromine Compounds Ltd.), discloses a method of making a physically strong, solid tablet having a mixture of halogenated 5,5-dimethylhydantoin and chlorine biocide compound. Specific ratios of BCDMH and TCCA are also disclosed. The disclosure is mainly for water treatment like industrial water, waste water, pulp & paper industry process water, cooling towers, swimming pools, spas and institutional and domestic applications and the like and hence the tablet size is large and is about 10-300 g in weight.
In a gravity fed water purification device, unlike the proposed use suggested in the prior art which is for a pool of water such as a swimming pool or a spa or a cooling tower, the biocide tablet is eroded as the water to be purified passes over it in a controlled fashion thereby ensuring a reasonable constant contact surface area between water and biocide tablet so that the amount of biocide released into the water is more or less at a uniform concentration. The tablet is in contact with water for a period where about 1000-2000 liters of water are passed over it over 3-8 months. A biocide tablet that is used in a gravity fed water purification device is generally small sized and weighing about 2-8 g. It is necessary that in such a situation the tablets do not chip off or break off and if it does the concentration in that pool of water would be very high which is undesirable. Thus it is essential to ensure a reasonable constant contact surface area between water and biocide tablet, and thus maintaining the tablet integrity becomes very important.
The present inventors have found that use of a combination of a halogenated 5,5-dialkyllhydantoin and a chlorine biocide compound such as TCCA and NaDCC, provide superior benefits in purifying water and making it microbiologically safe. However, manufacturing tablets of smaller size using the combination of a halogenated 5,5-dialkyllhydantoin and chlorine biocide compound is a problem as the tablet strength gets affected and the tablets are very brittle and thus break very easily.
The present inventors have found that by selecting a specific range of particle size of the materials and using a water soluble boron containing compound at selected range it is possible to obtain tablets weighing 2-8 g with good tablet strength, comprising a mixture of a halogenated 5,5-dialkyllhydantoin and a chlorine biocide compound. These tablets maintain the integrity of the tablets even when they are in continuous contact in water and they also have uniform erosion properties even when they are immersed in a stream of water for a prolonged period of time by maintaining a constant contact surface area between water and biocide tablet.
It is thus the basic object of the present invention to provide a biocide tablet comprising one or more halogenated 5,5-dialkyllhydantoins and chlorine biocide compounds, weighing 2-8 g with good tablet strength.
Another object of the present invention is directed to provide a biocide tablet comprising one or more halogenated 5,5-dialkyllhydantoins and chlorine biocide compounds, weighing 2-8 g with good tablet strength, having uniform erosion properties even when they are immersed in a stream water for a prolonged period of time.
Yet another object of the present invention is to provide a uniform concentration of the biocide in water by maintaining good integrity and erosion properties of the tablets in a water purification device.